Field of the Invention
The present invention relates to a method and a device for supplying an electronic measurement system in a fitting, through which a fluid flows, with electric power which the fluid flowing through the fitting generates in a turbine.
Description of the Background Art
Flow meters of all types, for example, in drinking water lines, industrial water lines, natural gas pipelines, pipelines, etc., have the task of monitoring and measuring the flow of the fluid and storing the measured values. This occurred originally with mechanical measuring and storage devices, which had to be read on site. Because reading on site in many cases is laborious, time-consuming, and at times even dangerous, it soon became desirable to transmit stored measured values wirelessly via radio. The electric power required to operate the transmitting and receiving devices was initially provided via power supply lines or batteries. This entails considerable additional expenditures, however. Solutions were therefore sought to reduce this cost.
One solution to the problem is to allow the fluid itself to produce the required electric power. To this end, a turbine that drives a current generator is placed in the pipe through which the fluid flows. The measuring, storing, transmitting, and receiving devices can be operated in this way without electrical supply lines having to be laid or batteries replaced. Compare, for example, GB 1 354 411 A1, FR 2 686 376 A, or U.S. Pat. No. 4,740,711 A.
It is also already known to supply electrical or electronic components in domestic water fittings with current in the same way. Thus, for example, WO 85/01337 A shows a water dispenser whose water flow can be turned on and off by an electrically controllable valve. A turbine wheel, which is impinged by water and drives a low-power electric generator, is disposed in the flow channel of the water dispenser. The generator is connected to a control device which controls the valve and whose battery can be charged with the power supplied by the generator. The flow channel of the water dispenser has a curvature of 90°, whereby the rotation axis of the turbine wheel coincides with the longitudinal axis of the tubular housing bounding the flow channel in this area. The generator is provided with the turbine flush-aligned outside the housing in the area of the 90° curvature, whereby an opening for passing through the generator shaft, coupled to the drive shaft of the turbine wheel, is provided in the housing. The shaft passage is sealed by a stuffing box.
A disadvantageous aspect of this solution in one respect is the need for a stuffing box seal whose lifetime is known to be limited. A further disadvantage is the required battery, because its lifetime is limited as well.
EP 0 361 333 A1, which corresponds to U.S. Pat. No. 4,963,780, shows a similar design. It as well uses a stuffing box seal between the turbine wheel and the current generator.
EP 0 793 330 A1, which corresponds to U.S. Pat. No. 6,011,334, discloses a current generator which can be installed in a pipe through which a fluid flows and which does not use a stuffing box seal. To this end, the pipe is non-magnetic in the area of the generator. A turbine wheel and a permanent magnet coupled to the turbine wheel are located in the interior of the pipe. The coil in which electric power is produced is located outside the pipe.
Comparable current generators are also installed in thermostatic valves of heating systems. Compare WO 2010/057957 A1, JP 2004-234431 A, or DE 101 32 682 C1. These also require batteries, because the hot water flow is interrupted at times.
The solutions described above are based on the principle that has been put into practice for over 100 years worldwide in hydroelectric plants. In this regard, water is held back to the highest possible potential level by a water-retaining structure. The energy of the movement of the flowing-off water is transferred to a water turbine or a water wheel, as a result of which it is caused to rotate at high torque. This in turn is passed on directly or via a gear mechanism to the shaft of a generator which converts the mechanical energy into electric power. The output of the hydroelectric power plants depends on the water flow, the drop height, and on the efficiency of the feed, the water turbine, the gear mechanism, the generator, and the transformer. Modern hydroelectric power plants achieve an efficiency of up to 90%.
Power plants operated with compressed air function according to the same principle.
The hydroelectric and compressed air power plants are thus constructed and controlled such that the turbine and with it the generator run at a constant network rotational speed, irrespective of whether a great deal or little electric power is taken off. At the same time, the generator is controlled so that it delivers a constant supply voltage. Known power plants therefore have a series of electronic and mechanical measuring and control equipment.
In the home, trades, and industry, a great number of consumption meters for fluids are employed, for example, for recording the consumption of fresh water, industrial water, heat, natural gas, oil, oxygen, etc. These measuring devices must function for a certain time, for example, for 5 or 6 years. If these devices are equipped with electronic components for the measurement, storing, and teletransmission of the consumption data, an electric power source is necessary. At present, this is a battery. The fluid-driven generators mentioned above could not gain acceptance for the following reasons.
The main difficulty with the use of fluid-activated generators for supplying consumption measuring devices is the greatly scattering current per unit time. In a water consumption meter at the maximum flow rate of Qmax=3000 L/h at the maximum allowable pressure loss of 1 bar for water consumption meters, the value QN=1.5 can be reduced by a maximum hydraulic power of 83 W. A turbine can be driven with this 83 W, which for its part drives the current generator, which can supply its current to the measuring, storing, transmitting, and receiving electronics. In practice, however, the maximum flow rate Qmax is achieved only very rarely. Typically, the flow volumes are much lower. The result of this is that the current generator can deliver only a fraction of the indicated maximum power. Thus, the water flow at a flow rate of 300 L/h and a pressure loss of 0.01 bar generates a hydraulic power of only 83 mW. If the flow rate drops even further, the generator no longer generates sufficient current to operate the electronics. At times, the flow rate is zero.
Moreover, water consumption meters are subject to the legal provision that the pressure loss in a water meter may not exceed a predetermined value (at present 1 bar).